Electrically conductive resin compositions are widespread in industry and utilized for various uses and particularly for uses requiring electrical conductivity. As the electrically conductive resin compositions, various compositions each containing resin and a large amount of an electrically conductive filler such as carbon black added thereto are known. Because the electrically conductive resin compositions are economically excellent, they are widely utilized mainly in industry.
In recent years, electrically conductive polymer materials have spread in packaging industry of IC chips, and a variation of the electrically conductive polymer materials is diversified from general-purpose plastics to engineering plastics. It has become increasingly important to take measures for controlling the electrical conductivity of precision equipment and those of peripheral devices disposed on the periphery thereof. As electrically conductive fillers for the electrically conductive polymer materials, in addition to carbon black, carbon fibers, graphite, metal coating fillers, metal fibers, and the like are used widely and properly in dependence on purposes and functions. But the electrically conductive fillers have problems that they deteriorate mechanical properties of the polymer materials and cause moldability to be difficult.
Polyethylene (hereinafter referred to as PE) resin is excellent in its friction and wear properties and mechanical strength and thus widely applied. In addition, an electrically conductive PE resin composition containing the electrically conductive filler has also widely spread. In recent years, with the spread of the precision equipment, a higher electrical conductivity control function is demanded, and thus low friction and wear properties and a stable electrical conductivity are demanded more than ever. A complex composed of the PE resin and the electrically conductive filler represented by carbon black has excellent electrical conductivity and is thus effective for applications requiring electrical conductivity.
For example, an electrically conductive complex composed of ultra-high-molecular-weight polyethylene (hereinafter referred to as UHMWPE) and granular glassy carbon is known (see patent document 1). The electrically conductive complex has a positive characteristic temperature coefficient showing a very large maximum change rate of resistance in a very narrow temperature range.
An electrically conductive thermoplastic resin composition containing 100 parts by weight of PE-based resin having a density of 0.84 to 0.90 g/cm3 and 50 to 1000 parts by weight of a metal filler and/or carbon black is also known (see patent document 2). The electrically conductive thermoplastic resin composition is excellent in molding processability such as in injection molding processability.
An electrically semi-conductive UHMWPE composition, having a specific volume resistivity of 105 to 109 Ω·cm, which contains the UHMWPE having a weight average molecular weight of not less than 5.0×105 and a polydispersity degree in the range of 15 to 100 and Ketjenblack dispersed in the UHMWPE is also known (see patent document 3). At the time of the production of the electrically semi-conductive UHMWPE composition, the UHMWPE and the Ketjenblack are fused and kneaded by using a screw extruder.